Wrong return value when multiplying - javascript

The output of console.log() is the value of width when I use the getRatioValue() function to multiply the inserted value of height and the calculated ratio. I cannot find why this is happening.
var soFunction = function(args) {
this.width = args.width || 0;
this.height = args.height || 0;
this.getRatioValue = function(value) {
var ratio = this.width / this.height;
return value * ratio;
};
console.log(this.getRatioValue(this.height)); // returns 1200
}
// Initialize object
var test = new soFunction({width: 1200, height: 980});

It is an simple mathematic operation. If you will write your function on one line you will get.
value is equal to height, so
return this.height * this.width / this.height
this.height's destroy each other and it returns the this.width

Related

How to add a custom position inside a forEach loop for each Canvas DrawImage?

I am trying to display multiple images using Canvas DrawImages with each a unique position. I have created an array with multiple images and I would like to position them on different parts of the canvas on load.
Now, all the canvas images are stacked on each other.
This is my JS:
(() => {
// Canvas Setup
let canvas = document.getElementById('hedoneCanvas');
let context = canvas.getContext('2d');
// // Canvas Images
let imageSources = [
'https://images.pexels.com/photos/1313267/pexels-photo-1313267.jpeg?cs=srgb&dl=food-fruit-green-1313267.jpg&fm=jpg',
'https://images.pexels.com/photos/2965413/pexels-photo-2965413.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940',
'https://images.pexels.com/photos/2196602/pexels-photo-2196602.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940',
'https://images.pexels.com/photos/2955490/pexels-photo-2955490.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940'
];
// Canvas Size
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
const loadImage = imagePath => {
return new Promise((resolve, reject) => {
let image = new Image();
image.addEventListener('load', () => {
resolve(image);
});
image.addEventListener('error', err => {
reject(err);
});
image.src = imagePath;
});
};
const canvasOnResize = () => {
canvas.width = window.innerWidth;
canvas.style.width = window.innerWidth;
canvas.height = window.innerHeight;
canvas.style.height = window.innerHeight;
};
window.addEventListener('resize', canvasOnResize);
Promise.all(imageSources.map(i => loadImage(i)))
.then(images => {
images.forEach(image => {
console.log(context);
context.drawImage(image, 0, 0, canvas.width, canvas.height);
});
})
.catch(err => {
console.error(err);
});
})();
I also want to make them responsive how can I archive this?
I have demo on Codepen: https://codepen.io/Merdzanovich/pen/dybLQqL
Trying to do something like this on hover:
http://vlnc.studio/
Responsive canvas
To make the content of a canvas responsive it is best to use a reference display size. This represents the ideal display size that your content is viewed in.
The reference is used to then calculate how to display the content on displays that do not match the ideal size.
In the example below the object reference defines the reference display and provides methods to resize the canvas and scale and position the content.
With the reference defined you can then position and size your content for the reference display.
For example the constant imageMaxSize = 512 sets the max size (width or height) of an image. The 512 is relative to the reference display (1920, 1080). The actual size that the image is display depends on the size of the page.
It sets a matrix that is used to transform the content to fit the display. Rather then use the top left of the display as origin (0,0) it sets the center of the canvas as the origin.
The example lets you set how the canvas responds to the display resolution, the const scaleMethod can be set to
"fit" will ensure that all the content will be displayed (as long as it fits the reference). However there may be blank areas above below or left and right of the content if the display aspect is different from the reference.
"fill" will ensure that the content will fill the display. However some of the content (top and bottom, or left and right) may be clipped if the display aspect does not match the reference.
Positioning images.
That just requires an array that holds the image position and size relative to the reference display.
In the example the array displayList which extends an array has the function
add(image,x,y) that adds an image to the list. The x and y represent the position of the image center and is relative to the reference display origin (center of canvas)
When an images is added its reference size is calculated from its natural size
draw(ctx) will draw all the items in the display list using the reference matrix to scale and position the images.
Rendering
Rather than render to the canvas ad-hock a render loop is used updateCanvas that ensures content is updated in sync with the display hardware. The ensure that if you have animated content it does not produce artifacts (shearing, flicker)
To prevent the rendering to needlessly draw content the render loop will only render the content when the semaphore update is set to true. For example when resizing the canvas the content needs to be rendered. This is achieved by simply setting update=true
Rather than use the resize event to resize the canvas, the render loop checks if the canvas size matches the page size. If there is a miss match then the canvas is resize. this is done because the resize event is not synced with the display hardware and will cause poor quality rendering while the display is being resized. it also ensures that the canvas is not resized more than once between display frames.
Example
requestAnimationFrame(updateCanvas);
const ctx = canvas.getContext('2d');
const SCALE_METHOD = "fit";
const images = [];
const ALPHA_FADE_IN_SPEED = 0.04; // for fade in out approx time use
// seconds = (0.016666 / ALPHA_FADE_IN_SPEED)
const FADE_OVERLAP = 0.4; // fraction of fade time. NOT less or equal to
// ALPHA_FADE_IN_SPEED and not greater equal to 0.5
const IMAGE_MAX_SIZE = 480; // image isze in pixel of reference display
const IMAGE_MIN_SIZE = IMAGE_MAX_SIZE * 0.8;
const IMAGE_SCALE_FLICK = IMAGE_MAX_SIZE * 0.05;
// sigmoid curve return val 0-1. P is power.
// 0 < p < 1 curve eases center
// 1 == p linear curve
// 1 < p curve eases out from 0 and into 1
Math.sCurve = (u, p = 2) => u <= 0 ? 0 : u >= 1 ? 1 : u ** p / (u ** p + (1 - u) ** p);
// Simple spring
// constructor(u,[a,[d,[t]]])
// u is spring position
// a is acceleration default 0.1
// d is dampening default 0.9
// t is spring target (equalibrium) default t = u
// properties
// u current spring length
// flick(v) // adds movement to spring
// step(u) gets next value of spring. target defaults to this.target
Math.freeSpring = (u, a = 0.3 , d = 0.65, t = u) => ({
u,
v : 0,
set target(v) { t = v },
flick(v) { this.v = v * (1/d) *(1/a)},
step(u = t) { return this.u += (this.v = (this.v += (u - this.u) * a) * d) }
})
var update = false;
const reference = {
get width() { return 1920 }, // ideal display resolution
get height() { return 1080 },
matrix: [1, 0, 0, 1, 0, 0],
resize(method, width = innerWidth, height = innerHeight) {
method = method.toLowerCase();
var scale = 1; // one to one of reference
if (method === "fit") {
scale = Math.min(width / reference.width, height / reference.height);
} else if (method === "fill") {
scale = Math.max(width / reference.width, height / reference.height);
}
const mat = reference.matrix;
mat[3] = mat[0] = scale;
mat[4] = width / 2;
mat[5] = height / 2;
canvas.width = width;
canvas.height = height;
update = true;
},
checkSize() {
if (canvas.width !== innerWidth || canvas.height !== innerHeight) {
reference.resize(SCALE_METHOD);
}
},
};
{
let count = 0;
[
'https://images.pexels.com/photos/1313267/pexels-photo-1313267.jpeg?cs=srgb&dl=food-fruit-green-1313267.jpg&fm=jpg',
'https://images.pexels.com/photos/2965413/pexels-photo-2965413.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940',
'https://images.pexels.com/photos/2196602/pexels-photo-2196602.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940',
'https://images.pexels.com/photos/2955490/pexels-photo-2955490.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940'
].forEach(src => {
count++;
const img = new Image;
img.src = src;
img.addEventListener("load", () => {
images.push(img);
if (! --count) { setup() }
})
img.addEventListener("error", () => {if (! --count) { setup() }});
});
}
const displayList = Object.assign([], {
add(image, x, y) {
var item;
var w = image.naturalWidth;
var h = image.naturalHeight;
const scale = Math.min(IMAGE_MAX_SIZE / w, IMAGE_MAX_SIZE / h);
w *= scale;
h *= scale;
displayList.push(item = {
image, x, y, w, h,
fading: false,
alpha: 0,
alphaStep: 0,
onAlphaReady: undefined,
scaleFX: Math.freeSpring(IMAGE_MIN_SIZE)
});
displayList.fadeQueue.push(item);
return item;
},
fadeQueue: [],
draw(ctx) {
var curvePower = 2
ctx.setTransform(...reference.matrix);
for (const item of displayList) {
if (item.fading) {
item.alpha += item.alphaStep;
curvePower = item.alphaStep > 0 ? 2 : 2;
if (item.onAlphaReady && (
(item.alphaStep < 0 && item.alpha <= FADE_OVERLAP) ||
(item.alphaStep > 0 && item.alpha >= 1 - FADE_OVERLAP))) {
item.onAlphaReady(item);
item.onAlphaReady = undefined;
} else if (item.alpha <= 0 || item.alpha >= 1) {
item.fading = false;
}
update = true;
}
ctx.globalAlpha = Math.sCurve(item.alpha, curvePower);
const s = item.scaleFX.step() / IMAGE_MAX_SIZE;
ctx.drawImage(item.image, item.x - item.w / 2 * s, item.y - item.h / 2 * s, item.w * s, item.h * s);
}
ctx.globalAlpha = 1;
ctx.setTransform(1, 0, 0, 1, 0, 0); // default transform
}
});
function fadeNextImage() {
const next = displayList.fadeQueue.shift();
if(next.alpha < 0.5) { // Start fade in
next.scaleFX.flick(IMAGE_SCALE_FLICK);
next.scaleFX.target = IMAGE_MAX_SIZE;
next.alphaStep = ALPHA_FADE_IN_SPEED;
} else { // Start fade out
next.scaleFX.flick(IMAGE_SCALE_FLICK);
next.scaleFX.target = IMAGE_MIN_SIZE;
next.alphaStep = -ALPHA_FADE_IN_SPEED;
}
next.onAlphaReady = fadeNextImage;
next.fading = true;
displayList.fadeQueue.push(next);
}
function setup() {
const repeat = 2;
var i, len = images.length;
const distX = (reference.width - IMAGE_MAX_SIZE) * 0.45;
const distY = (reference.height - IMAGE_MAX_SIZE) * 0.45;
for (i = 0; i < len * repeat; i++) {
const ang = i / (len * repeat) * Math.PI * 2 - Math.PI / 2;
displayList.add(images[i % len], Math.cos(ang) * distX, Math.sin(ang) * distY);
}
fadeNextImage();
}
function clearCanvas() {
ctx.globalAlpha = 1;
ctx.setTransform(1, 0, 0, 1, 0, 0);
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}
function loading(time) {
clearCanvas();
ctx.font = "12px arial";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.strokeStyle = "#aaa";
ctx.fillStyle = "white";
ctx.setTransform(1,0,0,1,ctx.canvas.width / 2, ctx.canvas.height / 2);
ctx.fillText("loading",0,0);
ctx.beginPath();
ctx.lineWidth = 2;
ctx.lineCap = "round";
const pos = time + Math.cos(time) * 0.25 + 1;
ctx.arc(0 ,0, 24, pos, pos + Math.cos(time * 0.1) * 0.5 + 1);
ctx.stroke();
}
function updateCanvas(time) {
reference.checkSize()
if(!displayList.length) {
loading(time / 100);
} else if (update) {
update = false;
clearCanvas();
displayList.draw(ctx);
}
requestAnimationFrame(updateCanvas);
}
canvas {
position: absolute;
top: 0px;
left: 0px;
background: black;
}
<canvas id="canvas"></canvas>
Try this:
Promise.all(imageSources.map(i => loadImage(i)))
.then(images => {
images.forEach((image,key) => {
context.drawImage(image, key*100, key*100, canvas.width, canvas.height);
});
})
.catch(err => {
console.error(err);
});

Image resizing before uploading by using HTML5 Canvas and javascript [duplicate]

I'm trying to create a thumbnail image on the client side using javascript and a canvas element, but when I shrink the image down, it looks terrible. It looks as if it was downsized in photoshop with the resampling set to 'Nearest Neighbor' instead of Bicubic. I know its possible to get this to look right, because this site can do it just fine using a canvas as well. I've tried using the same code they do as shown in the "[Source]" link, but it still looks terrible. Is there something I'm missing, some setting that needs to be set or something?
EDIT:
I'm trying to resize a jpg. I have tried resizing the same jpg on the linked site and in photoshop, and it looks fine when downsized.
Here is the relevant code:
reader.onloadend = function(e)
{
var img = new Image();
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
var copyContext = canvasCopy.getContext("2d");
img.onload = function()
{
var ratio = 1;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
};
img.src = reader.result;
}
EDIT2:
Seems I was mistaken, the linked website wasn't doing any better of a job of downsizing the image. I tried the other methods suggested and none of them look any better. This is what the different methods resulted in:
Photoshop:
Canvas:
Image with image-rendering: optimizeQuality set and scaled with width/height:
Image with image-rendering: optimizeQuality set and scaled with -moz-transform:
Canvas resize on pixastic:
I guess this means firefox isn't using bicubic sampling like its supposed to. I'll just have to wait until they actually add it.
EDIT3:
Original Image
So what do you do if all the browsers (actually, Chrome 5 gave me quite good one) won't give you good enough resampling quality? You implement them yourself then! Oh come on, we're entering the new age of Web 3.0, HTML5 compliant browsers, super optimized JIT javascript compilers, multi-core(†) machines, with tons of memory, what are you afraid of? Hey, there's the word java in javascript, so that should guarantee the performance, right? Behold, the thumbnail generating code:
// returns a function that calculates lanczos weight
function lanczosCreate(lobes) {
return function(x) {
if (x > lobes)
return 0;
x *= Math.PI;
if (Math.abs(x) < 1e-16)
return 1;
var xx = x / lobes;
return Math.sin(x) * Math.sin(xx) / x / xx;
};
}
// elem: canvas element, img: image element, sx: scaled width, lobes: kernel radius
function thumbnailer(elem, img, sx, lobes) {
this.canvas = elem;
elem.width = img.width;
elem.height = img.height;
elem.style.display = "none";
this.ctx = elem.getContext("2d");
this.ctx.drawImage(img, 0, 0);
this.img = img;
this.src = this.ctx.getImageData(0, 0, img.width, img.height);
this.dest = {
width : sx,
height : Math.round(img.height * sx / img.width),
};
this.dest.data = new Array(this.dest.width * this.dest.height * 3);
this.lanczos = lanczosCreate(lobes);
this.ratio = img.width / sx;
this.rcp_ratio = 2 / this.ratio;
this.range2 = Math.ceil(this.ratio * lobes / 2);
this.cacheLanc = {};
this.center = {};
this.icenter = {};
setTimeout(this.process1, 0, this, 0);
}
thumbnailer.prototype.process1 = function(self, u) {
self.center.x = (u + 0.5) * self.ratio;
self.icenter.x = Math.floor(self.center.x);
for (var v = 0; v < self.dest.height; v++) {
self.center.y = (v + 0.5) * self.ratio;
self.icenter.y = Math.floor(self.center.y);
var a, r, g, b;
a = r = g = b = 0;
for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
if (i < 0 || i >= self.src.width)
continue;
var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
if (!self.cacheLanc[f_x])
self.cacheLanc[f_x] = {};
for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
if (j < 0 || j >= self.src.height)
continue;
var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
if (self.cacheLanc[f_x][f_y] == undefined)
self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio, 2)
+ Math.pow(f_y * self.rcp_ratio, 2)) / 1000);
weight = self.cacheLanc[f_x][f_y];
if (weight > 0) {
var idx = (j * self.src.width + i) * 4;
a += weight;
r += weight * self.src.data[idx];
g += weight * self.src.data[idx + 1];
b += weight * self.src.data[idx + 2];
}
}
}
var idx = (v * self.dest.width + u) * 3;
self.dest.data[idx] = r / a;
self.dest.data[idx + 1] = g / a;
self.dest.data[idx + 2] = b / a;
}
if (++u < self.dest.width)
setTimeout(self.process1, 0, self, u);
else
setTimeout(self.process2, 0, self);
};
thumbnailer.prototype.process2 = function(self) {
self.canvas.width = self.dest.width;
self.canvas.height = self.dest.height;
self.ctx.drawImage(self.img, 0, 0, self.dest.width, self.dest.height);
self.src = self.ctx.getImageData(0, 0, self.dest.width, self.dest.height);
var idx, idx2;
for (var i = 0; i < self.dest.width; i++) {
for (var j = 0; j < self.dest.height; j++) {
idx = (j * self.dest.width + i) * 3;
idx2 = (j * self.dest.width + i) * 4;
self.src.data[idx2] = self.dest.data[idx];
self.src.data[idx2 + 1] = self.dest.data[idx + 1];
self.src.data[idx2 + 2] = self.dest.data[idx + 2];
}
}
self.ctx.putImageData(self.src, 0, 0);
self.canvas.style.display = "block";
};
...with which you can produce results like these!
so anyway, here is a 'fixed' version of your example:
img.onload = function() {
var canvas = document.createElement("canvas");
new thumbnailer(canvas, img, 188, 3); //this produces lanczos3
// but feel free to raise it up to 8. Your client will appreciate
// that the program makes full use of his machine.
document.body.appendChild(canvas);
};
Now it's time to pit your best browsers out there and see which one will least likely increase your client's blood pressure!
Umm, where's my sarcasm tag?
(since many parts of the code is based on Anrieff Gallery Generator is it also covered under GPL2? I don't know)
† actually due to limitation of javascript, multi-core is not supported.
Fast image resize/resample algorithm using Hermite filter with JavaScript. Support transparency, gives good quality. Preview:
Update: version 2.0 added on GitHub (faster, web workers + transferable objects). Finally i got it working!
Git: https://github.com/viliusle/Hermite-resize
Demo: http://viliusle.github.io/miniPaint/
/**
* Hermite resize - fast image resize/resample using Hermite filter. 1 cpu version!
*
* #param {HtmlElement} canvas
* #param {int} width
* #param {int} height
* #param {boolean} resize_canvas if true, canvas will be resized. Optional.
*/
function resample_single(canvas, width, height, resize_canvas) {
var width_source = canvas.width;
var height_source = canvas.height;
width = Math.round(width);
height = Math.round(height);
var ratio_w = width_source / width;
var ratio_h = height_source / height;
var ratio_w_half = Math.ceil(ratio_w / 2);
var ratio_h_half = Math.ceil(ratio_h / 2);
var ctx = canvas.getContext("2d");
var img = ctx.getImageData(0, 0, width_source, height_source);
var img2 = ctx.createImageData(width, height);
var data = img.data;
var data2 = img2.data;
for (var j = 0; j < height; j++) {
for (var i = 0; i < width; i++) {
var x2 = (i + j * width) * 4;
var weight = 0;
var weights = 0;
var weights_alpha = 0;
var gx_r = 0;
var gx_g = 0;
var gx_b = 0;
var gx_a = 0;
var center_y = (j + 0.5) * ratio_h;
var yy_start = Math.floor(j * ratio_h);
var yy_stop = Math.ceil((j + 1) * ratio_h);
for (var yy = yy_start; yy < yy_stop; yy++) {
var dy = Math.abs(center_y - (yy + 0.5)) / ratio_h_half;
var center_x = (i + 0.5) * ratio_w;
var w0 = dy * dy; //pre-calc part of w
var xx_start = Math.floor(i * ratio_w);
var xx_stop = Math.ceil((i + 1) * ratio_w);
for (var xx = xx_start; xx < xx_stop; xx++) {
var dx = Math.abs(center_x - (xx + 0.5)) / ratio_w_half;
var w = Math.sqrt(w0 + dx * dx);
if (w >= 1) {
//pixel too far
continue;
}
//hermite filter
weight = 2 * w * w * w - 3 * w * w + 1;
var pos_x = 4 * (xx + yy * width_source);
//alpha
gx_a += weight * data[pos_x + 3];
weights_alpha += weight;
//colors
if (data[pos_x + 3] < 255)
weight = weight * data[pos_x + 3] / 250;
gx_r += weight * data[pos_x];
gx_g += weight * data[pos_x + 1];
gx_b += weight * data[pos_x + 2];
weights += weight;
}
}
data2[x2] = gx_r / weights;
data2[x2 + 1] = gx_g / weights;
data2[x2 + 2] = gx_b / weights;
data2[x2 + 3] = gx_a / weights_alpha;
}
}
//clear and resize canvas
if (resize_canvas === true) {
canvas.width = width;
canvas.height = height;
} else {
ctx.clearRect(0, 0, width_source, height_source);
}
//draw
ctx.putImageData(img2, 0, 0);
}
Try pica - that's a highly optimized resizer with selectable algorythms. See demo.
For example, original image from first post is resized in 120ms with Lanczos filter and 3px window or 60ms with Box filter and 0.5px window. For huge 17mb image 5000x3000px resize takes ~1s on desktop and 3s on mobile.
All resize principles were described very well in this thread, and pica does not add rocket science. But it's optimized very well for modern JIT-s, and is ready to use out of box (via npm or bower). Also, it use webworkers when available to avoid interface freezes.
I also plan to add unsharp mask support soon, because it's very useful after downscale.
I know this is an old thread but it might be useful for some people such as myself that months after are hitting this issue for the first time.
Here is some code that resizes the image every time you reload the image. I am aware this is not optimal at all, but I provide it as a proof of concept.
Also, sorry for using jQuery for simple selectors but I just feel too comfortable with the syntax.
$(document).on('ready', createImage);
$(window).on('resize', createImage);
var createImage = function(){
var canvas = document.getElementById('myCanvas');
canvas.width = window.innerWidth || $(window).width();
canvas.height = window.innerHeight || $(window).height();
var ctx = canvas.getContext('2d');
img = new Image();
img.addEventListener('load', function () {
ctx.drawImage(this, 0, 0, w, h);
});
img.src = 'http://www.ruinvalor.com/Telanor/images/original.jpg';
};
html, body{
height: 100%;
width: 100%;
margin: 0;
padding: 0;
background: #000;
}
canvas{
position: absolute;
left: 0;
top: 0;
z-index: 0;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<html>
<head>
<meta charset="utf-8" />
<title>Canvas Resize</title>
</head>
<body>
<canvas id="myCanvas"></canvas>
</body>
</html>
My createImage function is called once when the document is loaded and after that it is called every time the window receives a resize event.
I tested it in Chrome 6 and Firefox 3.6, both on the Mac. This "technique" eats processor as it if was ice cream in the summer, but it does the trick.
I've put up some algorithms to do image interpolation on html canvas pixel arrays that might be useful here:
https://web.archive.org/web/20170104190425/http://jsperf.com:80/pixel-interpolation/2
These can be copy/pasted and can be used inside of web workers to resize images (or any other operation that requires interpolation - I'm using them to defish images at the moment).
I haven't added the lanczos stuff above, so feel free to add that as a comparison if you'd like.
This is a javascript function adapted from #Telanor's code. When passing a image base64 as first argument to the function, it returns the base64 of the resized image. maxWidth and maxHeight are optional.
function thumbnail(base64, maxWidth, maxHeight) {
// Max size for thumbnail
if(typeof(maxWidth) === 'undefined') var maxWidth = 500;
if(typeof(maxHeight) === 'undefined') var maxHeight = 500;
// Create and initialize two canvas
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
var copyContext = canvasCopy.getContext("2d");
// Create original image
var img = new Image();
img.src = base64;
// Determine new ratio based on max size
var ratio = 1;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
// Draw original image in second canvas
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
// Copy and resize second canvas to first canvas
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
return canvas.toDataURL();
}
I'd highly suggest you check out this link and make sure it is set to true.
Controlling image scaling behavior
Introduced in Gecko 1.9.2 (Firefox 3.6
/ Thunderbird 3.1 / Fennec 1.0)
Gecko 1.9.2 introduced the
mozImageSmoothingEnabled property to
the canvas element; if this Boolean
value is false, images won't be
smoothed when scaled. This property is
true by default. view plainprint?
cx.mozImageSmoothingEnabled = false;
If you're simply trying to resize an image, I'd recommend setting width and height of the image with CSS. Here's a quick example:
.small-image {
width: 100px;
height: 100px;
}
Note that the height and width can also be set using JavaScript. Here's quick code sample:
var img = document.getElement("my-image");
img.style.width = 100 + "px"; // Make sure you add the "px" to the end,
img.style.height = 100 + "px"; // otherwise you'll confuse IE
Also, to ensure that the resized image looks good, add the following css rules to image selector:
-ms-interpolation-mode: bicubic: introduce in IE7
image-rendering: optimizeQuality: introduced in FireFox 3.6
As far as I can tell, all browsers except IE using an bicubic algorithm to resize images by default, so your resized images should look good in Firefox and Chrome.
If setting the css width and height doesn't work, you may want to play with a css transform:
-moz-transform: scale(sx[, sy])
-webkit-transform:scale(sx[, sy])
If for whatever reason you need to use a canvas, please note that there are two ways an image can be resize: by resizing the canvas with css or by drawing the image at a smaller size.
See this question for more details.
i got this image by right clicking the canvas element in firefox and saving as.
var img = new Image();
img.onload = function () {
console.debug(this.width,this.height);
var canvas = document.createElement('canvas'), ctx;
canvas.width = 188;
canvas.height = 150;
document.body.appendChild(canvas);
ctx = canvas.getContext('2d');
ctx.drawImage(img,0,0,188,150);
};
img.src = 'original.jpg';
so anyway, here is a 'fixed' version of your example:
var img = new Image();
// added cause it wasnt defined
var canvas = document.createElement("canvas");
document.body.appendChild(canvas);
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
// adding it to the body
document.body.appendChild(canvasCopy);
var copyContext = canvasCopy.getContext("2d");
img.onload = function()
{
var ratio = 1;
// defining cause it wasnt
var maxWidth = 188,
maxHeight = 150;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
// the line to change
// ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
// the method signature you are using is for slicing
ctx.drawImage(canvasCopy, 0, 0, canvas.width, canvas.height);
};
// changed for example
img.src = 'original.jpg';
For resizing to image with width less that original, i use:
function resize2(i) {
var cc = document.createElement("canvas");
cc.width = i.width / 2;
cc.height = i.height / 2;
var ctx = cc.getContext("2d");
ctx.drawImage(i, 0, 0, cc.width, cc.height);
return cc;
}
var cc = img;
while (cc.width > 64 * 2) {
cc = resize2(cc);
}
// .. than drawImage(cc, .... )
and it works =).
I have a feeling the module I wrote will produce similar results to photoshop, as it preserves color data by averaging them, not applying an algorithm. It's kind of slow, but to me it is the best, because it preserves all the color data.
https://github.com/danschumann/limby-resize/blob/master/lib/canvas_resize.js
It doesn't take the nearest neighbor and drop other pixels, or sample a group and take a random average. It takes the exact proportion each source pixel should output into the destination pixel. The average pixel color in the source will be the average pixel color in the destination, which these other formulas, I think they will not be.
an example of how to use is at the bottom of
https://github.com/danschumann/limby-resize
UPDATE OCT 2018: These days my example is more academic than anything else. Webgl is pretty much 100%, so you'd be better off resizing with that to produce similar results, but faster. PICA.js does this, I believe. –
The problem with some of this solutions is that they access directly the pixel data and loop through it to perform the downsampling. Depending on the size of the image this can be very resource intensive, and it would be better to use the browser's internal algorithms.
The drawImage() function is using a linear-interpolation, nearest-neighbor resampling method. That works well when you are not resizing down more than half the original size.
If you loop to only resize max one half at a time, the results would be quite good, and much faster than accessing pixel data.
This function downsample to half at a time until reaching the desired size:
function resize_image( src, dst, type, quality ) {
var tmp = new Image(),
canvas, context, cW, cH;
type = type || 'image/jpeg';
quality = quality || 0.92;
cW = src.naturalWidth;
cH = src.naturalHeight;
tmp.src = src.src;
tmp.onload = function() {
canvas = document.createElement( 'canvas' );
cW /= 2;
cH /= 2;
if ( cW < src.width ) cW = src.width;
if ( cH < src.height ) cH = src.height;
canvas.width = cW;
canvas.height = cH;
context = canvas.getContext( '2d' );
context.drawImage( tmp, 0, 0, cW, cH );
dst.src = canvas.toDataURL( type, quality );
if ( cW <= src.width || cH <= src.height )
return;
tmp.src = dst.src;
}
}
// The images sent as parameters can be in the DOM or be image objects
resize_image( $( '#original' )[0], $( '#smaller' )[0] );
Credits to this post
So something interesting that I found a while ago while working with canvas that might be helpful:
To resize the canvas control on its own, you need to use the height="" and width="" attributes (or canvas.width/canvas.height elements). If you use CSS to resize the canvas, it will actually stretch (i.e.: resize) the content of the canvas to fit the full canvas (rather than simply increasing or decreasing the area of the canvas.
It'd be worth a shot to try drawing the image into a canvas control with the height and width attributes set to the size of the image and then using CSS to resize the canvas to the size you're looking for. Perhaps this would use a different resizing algorithm.
It should also be noted that canvas has different effects in different browsers (and even different versions of different browsers). The algorithms and techniques used in the browsers is likely to change over time (especially with Firefox 4 and Chrome 6 coming out so soon, which will place heavy emphasis on canvas rendering performance).
In addition, you may want to give SVG a shot, too, as it likely uses a different algorithm as well.
Best of luck!
Fast and simple Javascript image resizer:
https://github.com/calvintwr/blitz-hermite-resize
const blitz = Blitz.create()
/* Promise */
blitz({
source: DOM Image/DOM Canvas/jQuery/DataURL/File,
width: 400,
height: 600
}).then(output => {
// handle output
})catch(error => {
// handle error
})
/* Await */
let resized = await blizt({...})
/* Old school callback */
const blitz = Blitz.create('callback')
blitz({...}, function(output) {
// run your callback.
})
History
This is really after many rounds of research, reading and trying.
The resizer algorithm uses #ViliusL's Hermite script (Hermite resizer is really the fastest and gives reasonably good output). Extended with features you need.
Forks 1 worker to do the resizing so that it doesn't freeze your browser when resizing, unlike all other JS resizers out there.
I converted #syockit's answer as well as the step-down approach into a reusable Angular service for anyone who's interested: https://gist.github.com/fisch0920/37bac5e741eaec60e983
I included both solutions because they both have their own pros / cons. The lanczos convolution approach is higher quality at the cost of being slower, whereas the step-wise downscaling approach produces reasonably antialiased results and is significantly faster.
Example usage:
angular.module('demo').controller('ExampleCtrl', function (imageService) {
// EXAMPLE USAGE
// NOTE: it's bad practice to access the DOM inside a controller,
// but this is just to show the example usage.
// resize by lanczos-sinc filter
imageService.resize($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
// resize by stepping down image size in increments of 2x
imageService.resizeStep($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
})
Thanks #syockit for an awesome answer. however, I had to reformat a little as follows to make it work. Perhaps due to DOM scanning issues:
$(document).ready(function () {
$('img').on("load", clickA);
function clickA() {
var img = this;
var canvas = document.createElement("canvas");
new thumbnailer(canvas, img, 50, 3);
document.body.appendChild(canvas);
}
function thumbnailer(elem, img, sx, lobes) {
this.canvas = elem;
elem.width = img.width;
elem.height = img.height;
elem.style.display = "none";
this.ctx = elem.getContext("2d");
this.ctx.drawImage(img, 0, 0);
this.img = img;
this.src = this.ctx.getImageData(0, 0, img.width, img.height);
this.dest = {
width: sx,
height: Math.round(img.height * sx / img.width)
};
this.dest.data = new Array(this.dest.width * this.dest.height * 3);
this.lanczos = lanczosCreate(lobes);
this.ratio = img.width / sx;
this.rcp_ratio = 2 / this.ratio;
this.range2 = Math.ceil(this.ratio * lobes / 2);
this.cacheLanc = {};
this.center = {};
this.icenter = {};
setTimeout(process1, 0, this, 0);
}
//returns a function that calculates lanczos weight
function lanczosCreate(lobes) {
return function (x) {
if (x > lobes)
return 0;
x *= Math.PI;
if (Math.abs(x) < 1e-16)
return 1
var xx = x / lobes;
return Math.sin(x) * Math.sin(xx) / x / xx;
}
}
process1 = function (self, u) {
self.center.x = (u + 0.5) * self.ratio;
self.icenter.x = Math.floor(self.center.x);
for (var v = 0; v < self.dest.height; v++) {
self.center.y = (v + 0.5) * self.ratio;
self.icenter.y = Math.floor(self.center.y);
var a, r, g, b;
a = r = g = b = 0;
for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
if (i < 0 || i >= self.src.width)
continue;
var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
if (!self.cacheLanc[f_x])
self.cacheLanc[f_x] = {};
for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
if (j < 0 || j >= self.src.height)
continue;
var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
if (self.cacheLanc[f_x][f_y] == undefined)
self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio, 2) + Math.pow(f_y * self.rcp_ratio, 2)) / 1000);
weight = self.cacheLanc[f_x][f_y];
if (weight > 0) {
var idx = (j * self.src.width + i) * 4;
a += weight;
r += weight * self.src.data[idx];
g += weight * self.src.data[idx + 1];
b += weight * self.src.data[idx + 2];
}
}
}
var idx = (v * self.dest.width + u) * 3;
self.dest.data[idx] = r / a;
self.dest.data[idx + 1] = g / a;
self.dest.data[idx + 2] = b / a;
}
if (++u < self.dest.width)
setTimeout(process1, 0, self, u);
else
setTimeout(process2, 0, self);
};
process2 = function (self) {
self.canvas.width = self.dest.width;
self.canvas.height = self.dest.height;
self.ctx.drawImage(self.img, 0, 0);
self.src = self.ctx.getImageData(0, 0, self.dest.width, self.dest.height);
var idx, idx2;
for (var i = 0; i < self.dest.width; i++) {
for (var j = 0; j < self.dest.height; j++) {
idx = (j * self.dest.width + i) * 3;
idx2 = (j * self.dest.width + i) * 4;
self.src.data[idx2] = self.dest.data[idx];
self.src.data[idx2 + 1] = self.dest.data[idx + 1];
self.src.data[idx2 + 2] = self.dest.data[idx + 2];
}
}
self.ctx.putImageData(self.src, 0, 0);
self.canvas.style.display = "block";
}
});
I wanted some well defined functions out of answers here so ended up with these which am hoping would be useful for others also,
function getImageFromLink(link) {
return new Promise(function (resolve) {
var image = new Image();
image.onload = function () { resolve(image); };
image.src = link;
});
}
function resizeImageToBlob(image, width, height, mime) {
return new Promise(function (resolve) {
var canvas = document.createElement('canvas');
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(image, 0, 0, width, height);
return canvas.toBlob(resolve, mime);
});
}
getImageFromLink(location.href).then(function (image) {
// calculate these based on the original size
var width = image.width / 4;
var height = image.height / 4;
return resizeImageToBlob(image, width, height, 'image/jpeg');
}).then(function (blob) {
// Do something with the result Blob object
document.querySelector('img').src = URL.createObjectURL(blob);
});
Just for the sake of testing this run it on a image opened in a tab.
I just ran a page of side by sides comparisons and unless something has changed recently, I could see no better downsizing (scaling) using canvas vs. simple css. I tested in FF6 Mac OSX 10.7. Still slightly soft vs. the original.
I did however stumble upon something that did make a huge difference and that was using image filters in browsers that support canvas. You can actually manipulate images much like you can in Photoshop with blur, sharpen, saturation, ripple, grayscale, etc.
I then found an awesome jQuery plug-in which makes application of these filters a snap:
http://codecanyon.net/item/jsmanipulate-jquery-image-manipulation-plugin/428234
I simply apply the sharpen filter right after resizing the image which should give you the desired effect. I didn't even have to use a canvas element.
Looking for another great simple solution?
var img=document.createElement('img');
img.src=canvas.toDataURL();
$(img).css("background", backgroundColor);
$(img).width(settings.width);
$(img).height(settings.height);
This solution will use the resize algorith of browser! :)

Can i invoke this.method within constructor function

Im trying to invoke method inside constructor, is it not possible or have i missed something?
function Rectangle(height, width) {
this.height = height;
this.width = width;
this.calcArea = function() {
console.log(this.height);
return this.height * this.width;
};
this.calcArea(); // trying to do it here, its invoked but no result
}
var newone = new Rectangle(12,24);
You can try something like this:
function Rectangle(height, width) {
var self = this;
self.height = height;
self.width = width;
self.calcArea = (function() {
console.log(this.height);
return self.height * self.width;
})();
}
var newone = new Rectangle(12,24)
console.log(newone.calcArea);
Its working just fine. You are not using the returned value.
function Rectangle(height, width) {
this.height = height;
this.width = width;
this.calcArea = function() {
console.log(this.height);
return this.height * this.width;
};
var area =this.calcArea(); // trying to do it here, its invoked but no result
console.log(area); //288
}
var newone = new Rectangle(12,24);

Use canvas context works as global but not when I pass it

I'm working on a final project (interactive Javascript game, etc.) and decided to give myself a challenge by learning canvas and HTML5. I'm also trying to learn Javascript objects (and organize what so many people seem to throw into one big script tag), etc. so excuse some possible stupidity on my part. :)
So currently I have the core working but I'm trying to make a start screen (I'm going to blur a paused random game behind the start options). The game involves dodging obstacles. When I draw the obstacles using a global variable context everything works. When I try to pass in a variable it dies. Here's what works:
var mainCanvas = document.getElementById("objectsToAvoidCanvas");
var mainContext = mainCanvas.getContext('2d');
function Obstacle(){
var height;
var width;
var xPosition;
var yPosition;
var isOffScreen;
var isSafeToAddMore;
var speed;
var anonymousCreation = function(){
this.width = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
this.height = Math.floor((Math.random() * window.innerHeight * 0.7) + 1);
this.xPosition = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
this.yPosition = this.height * -1;
this.isOffScreen = false;
this.isSafeToAddMore = false;
this.speed = 1;
mainContext.fillStyle = '#009933';
mainContext.fillRect(this.xPosition, this.yPosition, this.width, this.height);
};
anonymousCreation();
};
Obstacle.prototype.drawInRandomPlace = function(){
yPosition = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
mainContext.fillStyle = '#009933';
mainContext.fillRect(xPosition, yPosition, width, height);
};
However, something along these lines breaks:
function Obstacle(context){
var height;
var width;
var xPosition;
var yPosition;
var isOffScreen;
var isSafeToAddMore;
var speed;
var mainCanvas
var mainContext
var anonymousCreation = function(){
this.mainContext = context
this.width = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
this.height = Math.floor((Math.random() * window.innerHeight * 0.7) + 1);
this.xPosition = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
this.yPosition = this.height * -1;
this.isOffScreen = false;
this.isSafeToAddMore = false;
this.speed = 1;
mainContext.fillStyle = '#009933';
mainContext.fillRect(this.xPosition, this.yPosition, this.width, this.height);
};
anonymousCreation();
};
Obstacle.prototype.drawInRandomPlace = function(){
yPosition = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
mainContext.fillStyle = '#009933';
mainContext.fillRect(xPosition, yPosition, width, height);
};
I've tried using this.mainContext = context or actually grabbing from a passed string document.getElementById(aString). Just a bunch of different variations, etc inside the constructor. Been working on this for over an hour and can't figure it out so I thought I'd ask you guys. Probably been staring at it for too long.
Thanks!
When you switched to this.mainContext, you didn't replace all other instances of mainContext:
var anonymousCreation = function(){
this.mainContext = context;
this.width = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
this.height = Math.floor((Math.random() * window.innerHeight * 0.7) + 1);
this.xPosition = Math.floor((Math.random() * window.innerWidth * 0.8) + 1);
this.yPosition = this.height * -1;
this.isOffScreen = false;
this.isSafeToAddMore = false;
this.speed = 1;
/* old
mainContext.fillStyle = '#009933';
mainContext.fillRect(this.xPosition, this.yPosition, this.width, this.height);
*/
this.mainContext.fillStyle = '#009933'; //added this.
this.mainContext.fillRect(this.xPosition, this.yPosition, this.width, this.height); //added this.
};
anonymousCreation();
};
this.mainContext = context is the guilty one. There's no context parameter to your anonymousCreation function. While sub-functions have access to variables declared with var, they can't access parameters from their parent function. I lied. I tested this and it seems to work.I don't really see the point of the subfunction though, but Javascript is a very loose language and you can do things in exotic fashions.
When you use "var" to declare content inside an object, you declare private members that won't be accessible from the outside. Unless you plan on making getters and setters, I don't recommend doing that systematically. I prefer doing this:
function MyObject(arg1, arg2) {
this.property1 = arg1;
this.property2 = arg2;
}
MyObject.prototype.myFunction = function(arg) {
console.log(this.property1 + this.property2);
};
sampleInstance = new MyObject(1, 2);

JavaScript sine wave

track : function(x, y, top, ampl) {
return {
top : top + 2,
x : x + ampl * Math.sin(top / 20),
y : (top / this.screenHeight < 0.65) ? y + 2 : 1 + y + ampl * Math.cos(top / 25)
};
}
This routine sends snowflakes flying in sine wave manner.
But how does it do that? Please explain.
It uses Math.sin for x; and Math.cos for y, but other snippets I've seen use them in the opposite way. Why? Why exactly top/20 and top/25?
The whole code:
<script type="text/javascript">
var snowflakes = { // Namespace
/* Settings */
pics : [
['snow.gif' , 24, 24],
['snow2.gif', 24, 24],
['snow3.gif', 24, 24]
],
track : function(x, y, top, ampl) {
return {
top : top + 2,
x : x + ampl * Math.sin(top / 20),
y : (top / this.screenHeight < 0.65) ? y + 2 : 1 + y + ampl * Math.cos(top / 25)
};
},
quantity : 30,
minSpeed : 20, // 1 - 100, minSpeed <= maxSpeed
maxSpeed : 40, // 1 - 100, maxSpeed >= minSpeed
isMelt : true, // true OR false
/* Properties */
screenWidth : 0,
screenHeight : 0,
archive : [],
timer : null,
/* Methods */
addHandler : function(object, event, handler, useCapture) {
if (object.addEventListener) object.addEventListener(event, handler, useCapture);
else if (object.attachEvent)object.attachEvent('on' + event, handler);
else object['on' + event] = handler;
},
create : function(o, index) {
var rand = Math.random();
this.timer = null;
this.o = o;
this.index = index;
this.ampl = 3 + 7*rand;
this.type = Math.round((o.pics.length - 1) * rand);
this.width = o.pics[this.type][1];
this.height = o.pics[this.type][2];
this.speed = o.minSpeed + (o.maxSpeed - o.minSpeed) * rand;
this.speed = 1000 / this.speed;
this.deviation = o.maxDeviation * rand;
this.x = o.screenWidth * rand - this.width;
this.y = 0 - this.height;
this.top = this.y;
this.img = document.createElement('img');
this.img.src = o.pics[this.type][0];
this.img.style.top = this.y + 'px';
this.img.style.position = 'absolute';
this.img.style.zIndex = 10000;
this.img.style.left = this.x + 'px';
this.img.obj = this;
if (o.isMelt) this.img.onmouseover = function() {
clearTimeout(this.obj.timer);
this.obj.timer = null;
this.parentNode.removeChild(this);
}
document.body.appendChild(this.img);
this.move();
},
init : function() {
this.screenWidth = window.innerWidth ? window.innerWidth : (document.documentElement.clientWidth ? document.documentElement.clientWidth : document.body.offsetWidth);
this.screenWidth = navigator.userAgent.toLowerCase().indexOf('gecko') == -1 ? this.screenWidth : document.body.offsetWidth;
this.screenHeight = window.innerHeight ? window.innerHeight : (document.documentElement.clientHeight ? document.documentElement.clientHeight : document.body.offsetHeight);
this.screenScroll = (window.scrollY) ? window.scrollY : document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop;
this.archive[this.archive.length] = new this.create(this, this.archive.length);
clearTimeout(this.timer);
this.timer = null
this.timer = setTimeout(function(){snowflakes.init()}, 60000 / this.quantity);
}
};
snowflakes.create.prototype = {
move : function() {
var newXY = this.o.track(this.x, this.y, this.top, this.ampl);
this.x = newXY.x;
this.y = newXY.y;
this.top = newXY.top;
if (this.y < this.o.screenHeight + this.o.screenScroll - this.height) {
this.img.style.top = this.y + 'px';
this.x = this.x < this.o.screenWidth - this.width ? this.x : this.o.screenWidth - this.width;
this.img.style.left = this.x + 'px';
var index = this.index;
this.timer = setTimeout(function(){snowflakes.archive[index].move()}, this.speed);
} else {
delete(this.o.archive[this.index]);
this.img.parentNode.removeChild(this.img);
}
}
};
snowflakes.addHandler(window, 'load', function() {snowflakes.init();});
snowflakes.addHandler(window, 'resize', function() {snowflakes.init();});
</script>
The basic sine function is defined as:
f(x) = A sin(wt + p)
where
A is the amplitude
w is the frequency
p is the phase
These factors determine how the graph of f will look like.
The amplitude can be thought of as a scaling factor, the larger A, the larger (absolute values) the peaks and lows of f.
The frequency determines how fast the sine function will run through all its values until it starts over again - sine is a periodic function. The larger k, the faster f will run through one period.
p is the phase, think of it as "shifting" the starting point of the function to the right (positive p) or left (negative). Hard to explain in words, have a look here for graphs.
The function you give in your example is a generalized version of
f: R->R², f(t)=(sin(t), cos(t))
Which is (one of) the parametrizations of the unit circle . If you increase t monotonously and plot x (sin(t)) and y (cos(t)) you will have a point flying on a circle with radius 1.
Your generalized function is
f: R->R², f(t) = (A sin(1/wt), A cos(1/wt)), w > 1
In your case A=ampl, t=top and w=20 for the x coordinate and w=25 for the y coordinate. These slight deviations for w are there make the movement jittery, so that it's no longer a perfect circle, but rather some "distorted" ellipse - snow flakes don't fall in perfect circles, I guess. Additionally this makes the path of the flake appear to be more random than straight perfect circles. It's an illusion though, this is all also very deterministic and still periodic - it's just that x and y movement are "out of phase" so it takes a whole lot longer until one period is completed.
w is chosen > 1 to "slow down" the circular movement. The larger you choose w, the lower the frequency will be and your moving point will complete a full circle much slower.
The larger you choose A, the larger your circle will become.
It just makes the sine wave bigger so the curves can be more easily observed.
Here's a fiddle I tried making. If I change 20 and 25 to 1, the movement gets less interesting. http://jsfiddle.net/AbM9z/1/
It would help to know what values the function is being called with.

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